The invention relates to an injection unit for an injection molding machine having a plasticising cylinder and a plasticising screw which is axially displaceably arranged therein, wherein the plasticising cylinder is fixedly connected to a housing which at two oppositely disposed walls carries a respective crank drive extending parallel to the wall for displacement of the plasticising screw, the crank drive being driven by a rotating motor mounted to the same wall.
In the known apparatuses of that kind, the motors for actuation of the crank drives are disposed outside the housing in which the crank drives are arranged. In order to save space, in that case (see EP 0 870 590 A2) the motors can be arranged in the direction of the axis of the machine. That however gives rise to the necessity to provide an expensive angle transmission between the motor and the crank drive.
In comparison therewith, the object of the present invention is to provide an arrangement which combines a low level of space requirement with a low level of structural complication and expenditure. In accordance with the invention that object is attained in that the motor is internally fixed to at least one of the walls and the axis of rotation of the motor extends normal to the crank drive.
Preferably, in such an apparatus, the crank drives will be arranged at the side walls of the housing and it will be provided that the crank drives extend vertically and that the motor extends above the plasticising screw in transverse relationship therewith. That makes it possible for the end of the plasticising screw to be supported in a vertical direction on a guide rail which is fixed with respect to the housing.
The most compact configuration for the apparatus according to the invention is achieved if there is provided at least one motor which has at both ends drive shafts which are mounted at mutually opposite walls of the housing. As the prices of the servo motors which can be used in accordance with the invention rise overproportionally with increasing power output, it may be desirable in that respect to arrange two such motors in mutually superposed relationship.